Is pneumonia contagious?

Pneumonia is inflammation (swelling) of the tissue in one or both of the lungs. It’s usually caused by an infection – most commonly, bacteria and viruses, which are contagious. It can also be caused by breathing in a foreign object (aspiration pneumonia) or, in rare cases, a fungal infection, which is not usually contagious.

Causes of pneumonia

Bacterial pneumonia

The most common cause of pneumonia in adults is a bacterium called Streptococcus pneumoniae. Other types of bacteria that can cause pneumonia include:

Viral pneumonia

Viruses can also cause pneumonia – most commonly, the respiratory syncytial virus (RSV), and sometimes the flu (influenza) type A or B virus.

Fungal pneumonia

In the UK, pneumonia caused by a fungal infection of the lungs is rare in people who are normally healthy. Pneumocystis jirovecii pneumonia remains the most common fungal pneumonia in people with low immune systems, such as those infected with HIV.

Aspiration pneumonia

Pneumonia can also be caused by breathing in a foreign object, such as a piece of food, or a harmful substance, such as smoke. This is called aspiration pneumonia. If breathing in a foreign object leads to a bacterial infection, this is contagious.

Catching pneumonia

The germs that can cause pneumonia are usually breathed in. People often have small amounts of germs in their nose and throat that can be passed on through:

coughs and sneezes – these launch tiny droplets of fluid containing germs into the air, which someone else can breathe in

touching an object and transferring germs onto it – someone else can touch this object, and then touch their own mouth or nose

Streptococcus pneumoniae bacteria, which causes most cases of pneumonia, is far less contagious than a cold or flu. This is because most people’s immune systems can kill the bacteria before they have the opportunity to cause an infection.

In rare cases, pneumonia can develop from an infection somewhere else in the body, when the germs enter the lungs through the bloodstream.

Vaccination

Some people are at higher risk of developing pneumonia. To help protect against pneumonia, it’s recommended that people at greater risk of complications, such as those who are 65 or over, should have: